The present invention relates to a silicon oxide film growing apparatus and, more particularly, to a liquid-phase selective silicon oxide film growing apparatus for selectively forming an insulating film on a semiconductor wafer.
In a conventional silicon oxide film growing apparatus, as shown in a sectional view of a main part in FIG. 2, a tank 1 comprises an immersing unit 19, a straightening unit 3, and a processing liquid adjustment unit 4. The immersing unit 19 is used for causing the processing tank 1 to immerse a semiconductor wafer 5 in a processing liquid. The straightening unit 3 is contiguous to the immersing unit 19 to straighten the flow of the processing liquid flowing into the immersing unit 19. The processing liquid adjustment unit 4 is contiguous to the immersing unit 19 to adjust the processing liquid flowing from the immersing unit 19.
The conventional apparatus includes a straightening plate 6 arranged at the boundary between the immersing unit 19 and the straightening unit 3, a liquid supply pipe 20 for supplying the processing liquid in the processing liquid adjustment unit 4 to the straightening unit 3, a liquid supply pump 11 and a processing liquid filter 12 arranged midway along the water supply pipe 20, and a processing liquid adjustment device 21, arranged in the processing liquid adjustment unit 4, for adding an aqueous boric acid solution to the processing liquid.
In addition, the processing tank 1 is arranged in a constant temperature tank 8 to keep the temperature of the processing liquid in the processing tank 1 to be constant (e.g., Japanese Utility Model Laid-Open Nos. 60-168574 and 63-102738). In order to adjust the processing liquid, it is proposed to immerse an aluminum plate in the processing liquid adjustment unit 4 in place of adding the aqueous boric acid solution to the processing liquid (e.g., Japanese Patent Laid-Open No. 3-21043).
A silicon oxide film growing apparatus aims at selectively depositing and growing a silicon oxide film on only a silicon oxide film on the surface of a semiconductor wafer in which a photoresist film pattern or a metal wiring pattern having a desired shape is formed on the silicon oxide film.
In the conventional silicon oxide film growing apparatus, however, since a method of entirely immersing the semiconductor wafer in the processing liquid is employed, the processing liquid is brought into contact with the rear surface of the semiconductor wafer.
Metal dust or photoresist dust is adhered to the rear surface of the semiconductor wafer. When the dust is mixed in the processing liquid, the service life of the processing liquid is disadvantageously shortened.
In addition, since the rear surface of the semiconductor wafer is not smoothed, a part of a silicon oxide film grown on the rear surface is peeled and drifts in the processing liquid as particles.
In the conventional silicon oxide film growing apparatus, although a processing tank and a processing liquid pipe consist of acrylic or vinyl chloride plastics, silicon oxides are easily precipitated on the surfaces of these materials from the processing liquid. For this reason, particles are produced, and the service life of the processing liquid is shortened.
In the conventional silicon oxide film growing apparatus, although a method of immersing a plurality of semiconductor wafers in one processing tank to grow silicon oxide films is employed, the entire silicon oxide film growing apparatus is occupied by a very small number of semiconductor wafers when various types of semiconductor wafers are produced in very small amounts. For this reason, the silicon oxide film growing apparatus has a drawback, i.e., very low productivity.
This drawback is a very serious problem in the present situation wherein liquid-phase growth of a silicon oxide film must be performed as long as several hours.
In addition, in the conventional silicon oxide film growing apparatus, selectivity for selectively growing a silicon oxide film on only a silicon oxide film on the surface of a semiconductor wafer is another problem.
According to an experiment performed by the present inventors, a growth rate of a silicon oxide film on the surface of a semiconductor wafer in an immersion unit was about 1,000 .ANG./h when the temperature of the processing liquid was 35.degree. C. In this case, particles each having a diameter of about 1,000 .ANG. were adhered to a photoresist pattern at 50,000 to 100,000 particles/mm.sup.2.
Thereafter, when the growth of the silicon oxide film is further continued, since silicon oxide films are grown on these particles, the silicon oxide films which can not be removed are finally adhered to the photoresist or a metal wiring layer, and a desired pattern can not be formed.